You just got unlucky!
Really really unlucky!!
You've sent your transaction when the mempool was quite empty and normally the tx would be accepted but just then a wave of transactions hit the chain, see the red circle.
~snip
Thanks for the graph, I want to ask some questions about what will happen those unconfirmed transactions around 1-6 satoshi/byte or more than that area, that is still unconfirmed?
Are those transactions will get confirm or will be back to every wallet of the sender? Like the transaction will fail since the transaction fees are too low. Is something like that? or they will wait until the transaction fees will drop around 1-6 satoshi per byte?